Lubricants containing a schiff base



United States Patent LUBRICANTS CQN'EAINING A SCHIFF BASE Kenneth L. McHugh, Kirkweod, Mo, and John 0. Smith, Swampscott, Mass assignors to Monsanto Research Corporation, t. Louis, Mo, a corporation of Delaware No Drawing. Filed Apr. 8, 1963, Ser. No. 271,498 7 Claims. (Cl. 252-515) This application is a continuation-in-part of my application Serial No. 79,503, tiled December 30, 1960, now abandoned. V

This invention relates to polyester compositions. More particularly, the invention relates to polyester lubricants comprising certain aldehyde-amine condensates as adjuvants therefor.

The accomplishments during the last decade of methods for developing thrust, as, for example, by the use of gas turbines, jet engines, and rockets, have created a demandfor lubricant compositions which will perform satisfactorily under conditions far more rigorous than ever contemplated in the past. The tremendous thrusts developed by such engines have necessitated that the lubricants be subjected to elevated temperature conditions, invariably resulting in increased oxidation of the lubricant, with the formation of corrosive materials which attack the metal parts of the engines. Thus, conventional lubricants can not be satisfactorily used under these conditions where the lubricants are commonly subjected to temperatures above 400 F. and, oftentimes above 500 F. Also, conventional adjuvants, e.g., oxidation and corrosion inhibitors incorporated in the known lubricants are usually inetiective under these more severe conditions of operation even though the lubricant base itself may be suitable.

An object of this invention is to provide an effective oxidation and corrosion inhibitor for use in polyester lubricants.

Another object of this invention is to provide polyester lubricant compositions having improved antioxidant and anticorrosion properties.

Another object of this invention is to provide polyester lubricant compositions having exceptional characteristics for use at elevated temperatures.

These and other objects hereinafter disclosed are provided by the invention wherein there is provided a lubricant composition consisting essentially of a polyester lubricant base stock and a minor proportion, sufiicient to inhibit oxidation, of an N,N-dibenzylideneplienylenediamine of the formula wherein R and R are selected from the class consisting of hydrogen, lower alkoxy and hydroxy and in which R and R when taken together represent the methylenedioxy radical, wherein R is alkoxy only when R at the same benzene ring is hydroxy, and wherein only one of R and R can be hydrogen when attached to the same benzene ring. By lower alkoxy is meant an alkoxy radical having from 1 to 6 carbon atoms.

The presently employed N,N-dibenzylidenephenylenediamines are prepared by methods which are well known in the art, e.g., by condensation of phenylenediamine with the appropriately substituted benzaldehyde. Examples of some suitable substituted benzaldehydes are 3-ethoxy-4- hydroxybenzaldehyde, 2-hydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde and 3,4-methylenedioxybenzaldehyde. The amine reacted with the aromatic aldehyde may be either 0-, mor p-phenylenediarnine; however, the amino groups are preferably in the para positions.

Bidifi Patented Aug. 17, l fihi Specific examples of some N,N-dibenzylidenephenylenediamine additives of this invention include:

N,N'-bis 2-ethoxy-3-hydroxybenzylidene -p-phenylenediamine N,N-bis (Z-hydroxy-3-pentyloxybenzylidene -p-phenylenediamine N,N '-bis 3 ,4-methylenedioxybenzylidene) -p-phenylenediamine N,N-bis (Z-hydroxybenzylidene -pphenylenediamine N,N-bis 3-isopropoxy-4-hydroxybenzyiidene -pphenylencdianiine N,N -bis 3 -ethoxy-2-hydroxybenzylidene -p-phenylenediamine N,N-bis 3 ,4-dihydroxybenzylidene -p-phenylenediamine The N,N'-dibenzylidenephenylenediamines may be prepared by heating stoichiometric amounts of the amine and the aldehyde at reflux temperature, usually within the range of from 20 C. to C., in the presence of a diluent, such as ethanol, isopropanol, hexane, octane, benzene, toluene, cyclohexane, and the like. After by-prodnot water has been removed, the diluent is removed by distillation to permit recovery of the dibenzylidene compounds. Other methods are also known to those skilled in the art for preparing these compounds and such methods may be used for preparing the additives for use in this invention.

Examples of polyester lubricants with which the present additives are advantageously employed are the liquid dior polyesters of dior polycarboxylic acids and mono-, dior polyhydric alcohols, or the esters of dior polyhydric alcohols and mono-carboxylic acids generally, such as bis(2-ethylhexyl) sebacate, azelate or adipate, dipropylene glycol dipelargonate, 1,6-hexamethylene glycol bis(2- ethylhexanoate), polyethylene glycol 2-ethylhexanoate, tridecyl pelargonate, bis(l-ethylpropyl) adipate or azelate, bis(2,2-dimethylhexyl) azelate, pentaerythritol tetravalerate or trimethylolpropane 2-ethylhexanoate, etc. Generally the polyester lubricant base stock is a polyester of a polyhydric alcohol containing 2 to 4 hydroxy groups and 2 to 10 carbons atoms and a fatty acid containing 4 to 22 carbon atoms.

The amount of N,N'-dibenzylidenephenylenediamine additive combined with the lubricant base stock may vary over wide limits depending upon the particular polyester lubricant base stock and the application to which the lubricant is to be subjected. In general, the amount of additive used is a minor proportion in comparison to the base stock but is an amount which is sufficient to impart antioxidant and corrosion resistance properties to the lubricant. Ordinarily, the phenylenediamine compound is combined with the base stock in an amount in the range of from about 0.01 to 10% by weight and preferably in the range of from about 0.1 to 3% by weight. In some compositions, the amount of the additive is limited by the solubility thereof in the lubricant base. Even though some of the present additives may exhibit only very limited solubility in some of the polyester lubricant bases, the limited amount of the additive dissolved in the base may still be sufiicient to improve the antioxidant and corrosion resistance properties of the lubricant.

The polyester lubricant compositions of this invention may also contain other additive materials in order to enhance other characteristics of the lubricant. For example, mineral oil detergents, pour point depressants, oiliness agents, extreme pressure addition agents, blooming agents, compounds for enhancing the viscosity index of the oil, thickening agents, and the like, may be added to the lubricant composition consisting essentially of polyester lubricant base stock.

The polyester lubricant compositions of this invention find utility not only in low temperature applications,

but also in high temperature applications and conditions not normally associated with conventional practice. Thus, they may be used not only in the conventional reciprocating internal combustion engines, such as the automotive engine and the diesel engine, but also in gas turbine engines such as turbo-jet engines, turbo-fan engines, and turbo-prop engines. Also, these compositions may be employed in rocket type engines if desired. In addition, the presently provided polyester lubricant compositions of this invention can also be used as cable oils, electric switch oils, transformer oils, hydraulic oils, and other applications which are not primarily concerned with the development of motive power.

The advantages, desirability, and usefulness of this invention are illustrated in the following examples.

EXAMPLE 1 In this example, the antioxidant and anticorrosion effectiveness of several N,Nbenzylidenephenylenediamines of this invention and of. a commercial amine additive are determined in trirnethylolpropane caproate base stock at a concentration of 1.0 g. additive per 100 g. of base stock and at a temperature of 500 F. A modification of Fed- 41 will be noted from the data in Table I that the effect of the addition of 1% N.N'-bis(3 methoxy 4 hydroxybenzylidene)p-phenylene diamine to trimethylol propane ester is to give a viscosity change of 0.0% and a neutralization number of 69.55 as compared with a viscosity change of 217.6 and a neutralization number of 81.14 obtained by the addition of the phenyl-wnaphthylamine in an amount of 1.0% to the same base stock. Under the same conditions, a viscosity change of 157.6% and a neutralization number of 103.3 were obtained for the untreated base stock.

EXAMPLE 2 In this example, the antioxidant and anticorrosion effectiveness of N,N bis(3,4- methylenedioxybenzylidene)-p-phenylene diamine was determined in a pentaerythritol tetracaproate lubricant base at a temperature of 400 F. and compared with the untreated base stock and the same base stock containing phenyl-a-naphthylamine as the commercial additive. The standard oxidation-corrosion test noted in Example 1 was also used except that the test was conducted at a temperature of 400 F.:2 F. using an air-flow of 5.0105 liters per eral Test Method Standard No, 791, Method 5308A, de, hour of air. The data obtained are reported in Table II.

Table II Vi at 100 F, Change in wt. oi Metals Neut. No., Evap, Additive mg. percent Before After Change, KOH/ml. 011 Steel Al Ag Ti Percent N,N bis(3,4 methylene dioxybenzyli- 19. 79 19. 82 0. 0. 0. 09 0.00 +0. 05 +0. 02 +0. 02 0.82

dene)p-phenylenediamine 1 Phenyl-u-naphthylamine 19.30 20. 16 4. 0. 01 0. 26 0. 00 +0. 03 0. 02 +0. 02 1. None 19. 20 28. 50 47. 80 10. 80 0. 20 +0. 03 +0. 09 0. 02 +0. 02 l. 00

1 Concentration, 0.5 g./100 g.

vised by the Wright Air Development Center, Wright- Pattern Air Force Base, Ohio, and described in detail in WADC Report, Oxidation-Corrosion Micro Scale Test,

WADC TR-55-449, Part III, May 1956, by John B. Christian, was used wherein the lubricant to be tested was exposed to air at a flow rate of one liter per hour for a period of time of 24 hours at a temperature of 500 F. in the presence of copper, steel, aluminum, silver and titanium test specimens. Upon completion of this test, the viscosity change of the lubricant at 100 F., neutralization number of the lubricant, and the weight loss of the metal specimens were determined by evaluation of the Reasonable variation and modification of the invention as described are possible, the essence of which is that there have been provided lubricant compositions comprising a polyester lubricating oil base stock and certain N,N-dibenzylidenephenylenediamines as additives.

We claim:

1. A composition consisting essentially of polyester lubricating oil and a minor proportion, sufiicient to inhibit oxidation, of a condensation product of the formula oxidation-corrosion properties of the lubricant and are 50 I I reported in Table I. R B

Table l Vise, cs. at 100 F. Change in wt. of Metals Neut. No., Additive mg.

Before After Change, KOH/ml. Cu Steel A1 Ag Ti Percent N,N-bis(3-methoxy-4-hydroxybenzylidcne)p-phenylenediamine 16. 23 16. 23 0 69. 55 0. 12 0. 16 0. 04 0. 04 0. 04 N .N-bis(Z-methoxybenzyli dene)-p-phenylenediamine 15. 25. 42 61. 9 88. 20 0. 83 0. 12 +0.08 0. 00 +0. 08 Phenyl-a-naphthylarrune 15. 70 49. 87 217. 6 S1. 15 1. 10 +0. 51 +0. 12 +0. 04 +0. 08 NOHO 15.36 39. 56 157. 6 103.3 2. 5 8. 9 0. 16 +0.16 1- 5 The value of an additive in the inhibition of oxidation and corrosion can not be determined solely from one of these measurements because of the complex inner relationship present; however, in general, an additive is effective as an antioxidant and corrosion inhibitor if the viscosity change is a minimum, the neutralization number is low, and the change in weight of the metal test specimens is low in this test. In order to aid in the evaluation of the effectiveness of these additives, comparative data with a commercial additive, phenyl-a-naphthylamine, and the untreated base lubricant stock are also given. Thus, it

5 hibit oxidation, of NJ '-bis(3,4-rnetlrylenedioxybenzylidene -p-phenylenedian1ine.

4. A lubricant composition consisting essentially of polyester lubricating oil, and a minor proportion, sufficient to inhibit oxidation, of N,N-bis(3-n1ethoXy-4-hydroxybenzylidene -p-phenylenediamine.

5. The lubricant composition of claim 1 wherein said lubricating oil is a polyester of a polyhydric alcohol containing 2 to 4 hydroxy groups and 2 to 10 carbon atoms and a fatty acid containiing about 4 to 22 carbon atoms.

6. A lubricant composition consisting essentially of pentaerythritol tetracaproate and from 0.01 to 10% by Weight of the tetracaproate of N,N'-bis{3,4 methylenedioxybenzylidene) -p-phenylenediamine.

7. A lubricant composition consisting essentially of trimethylolpropane caproate and from 0.01 to 10% by Weight of the caproate of N,N-bis(3-methoxy-4-hydroxybenzylidene)-p-phenylenediamine.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES McTurk, Synthetic Lubricants, WADC Tech. Report 5388, October 1953, Wri ht Air Development Center, USAF, Wright-Patterson AFB, Ohio (October, 1953) (pages 29 and 52 pertinent).

20 DANIEL E. VVYMAN, Primary Examiner. 

1. A COMPOSITION CONSISTING ESSENTIALLY OF POLYESTER LUBRICATING OIL AND A MINOR PROPORTION, SUFFICIENT TO INHIBIT OXIDATION, OF A CONDENSATION PRODUCT OF THE FORMULA 